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add assembly stub for cramium boot

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this fixes a stability issue observed at boot
This commit is contained in:
bunnie 2024-10-24 01:29:04 +08:00
parent df44d62b1f
commit f9e99a4ff3
1 changed files with 55 additions and 0 deletions
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55
loader/src/asm.rs
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@ -12,6 +12,61 @@ pub extern "C" fn _start(_kernel_args: usize, loader_sig: usize) {
let _kernel_args = _kernel_args;
#[cfg(any(feature = "cramium-soc", feature = "cramium-fpga"))]
let _kernel_args = platform::FLASH_BASE + platform::KERNEL_OFFSET;
// Stub for clearing IFRAM & RAM on Cramium target. This is required
// to clear the parity check bits, which are randomly set on boot. System will
// eventually hang if these bits aren't cleared.
#[cfg(any(feature = "cramium-soc", feature = "cramium-fpga"))]
unsafe {
#[rustfmt::skip]
asm! (
// test if ifram is cleared
"li t0, 0x50000000",
"li t1, 0x50040000",
"60:",
"lw t2, 0(t0)",
// if not 0, jump to clearing routine
"bne x0, t2, 30f",
"addi t0, t0, 4",
// loop if we haven't checked all of ifram
"bltu t0, t1, 60b",
// if we got here, all of ifram was 0, continue with boot
"j 50f",
// clear ifram
"30:",
"sw x0, 0(t0)",
"addi t0, t0, 4",
"bltu t0, t1, 30b",
// clear main ram
"li t0, 0x61000000",
"li t1, 0x61200000",
"20:",
"sw x0, 0(t0)",
"addi t0, t0, 4",
"bltu t0, t1, 20b",
".word 0x500f",
// reset the system
"li t0, 0x40040080",
"li t1, 0x55aa",
"70:",
"sw t1, 0(t0)",
"j 70b", // loop forever trying to trigger the reset
// Note that BMX access is unstable at this point in time due to the
// high number of parity errors that were flooding the system. Thus,
// the system has to go through a reset cycle before any further progress
// can be made.
// --------------------------------
// system should be rebooting at this point, code after this
// is unreachabale
// --------------------------------
// continue on boot
"50:",
);
}
unsafe {
#[rustfmt::skip]
asm! (